BACKGROUND AND AIMS Within Chenopodioideae, Atripliceae have been distinguished by two bracteoles enveloping the female flowers/fruits, whereas in other tribes flowers are described as ebracteolate with persistent perianth. Molecular phylogenetic hypotheses suggest 'bracteoles' to be homoplastic. The origin of the bracteoles was explained by successive inflorescence reductions. Flower reduction was used to explain sex determination. Therefore, floral ontogeny was studied to evaluate the nature of the bracteoles and sex determination in Atripliceae. METHODS Inflorescences of species of Atriplex, Chenopodium, Dysphania and Spinacia oleracea were investigated using light microscopy and scanning electron microscopy. Key RESULTS The main axis of the inflorescence is indeterminate with elementary dichasia as lateral units. Flowers develop centripetally, with first the formation of a perianth primordium either from a ring primordium or from five individual tepal primordia fusing post-genitally. Subsequently, five stamen primordia originate, followed by the formation of an annular ovary primordium surrounding a central single ovule. Flowers are either initially hermaphroditic remaining bisexual and/or becoming functionally unisexual at later stages, or initially unisexual. In the studied species of Atriplex, female flowers are strictly female, except in A. hortensis. In Spinacia, female and male flowers are unisexual at all developmental stages. Female flowers of Atriplex and Spinacia are protected by two accrescent fused tepal lobes, whereas the other perianth members are absent. CONCLUSIONS In Atriplex and Spinacia modified structures around female flowers are not bracteoles, but two opposite accrescent tepal lobes, parts of a perianth persistent on the fruit. Flowers can achieve sexuality through many different combinations; they are initially hermaphroditic, subsequently developing into bisexual or functionally unisexual flowers, with the exception of Spinacia and strictly female flowers in Atriplex, which are unisexual from the earliest developmental stages. There may be a relationship between the formation of an annular perianth primordium and flexibility in floral sex determination.

Developing flowers are important sinks in Arabidopsis thaliana. Their energy demand is covered by assimilates which are synthesized in source leaves and transported via the vasculature. Assimilates are unloaded either symplastically through plasmodesmata or apoplastically by specific transport proteins. Here we studied the pathway of phloem unloading and post-phloem transport in developing gynoecia. Using phloem-mobile fluorescent tracers, we show that phloem unloading into cells of ovule primordia followed a symplastic pathway. Subsequently, the same tracers could not move out of phloem cells into mature ovules anymore. A further change in the mode of phloem unloading occurred after anthesis. In open flowers as well as in outgrowing siliques, the phloem was again unloaded via the symplast. This observed onset of symplastic phloem unloading was accompanied by a change in frequency of MP17-GFP-labeled plasmodesmata. We could also show that the change in cell-cell connectivity was independent of fertilization and increasing sink demand. The presented results indicate that symplastic connectivity is highly regulated and varies not only between different sink tissues but also between different developmental stages.

Summary Iron deficiency responses comprise molecular, physiological and developmental adjustments, ultimately leading to an improved cellular iron homeostasis. By using a proteomic approach, we identified the ubiquitin conjugating enzyme UBC13 as being highly responsive to the iron regime at the post-transcriptional level in tips of cucumber (Cucumis sativus) roots. UBC13 has been shown to catalyze noncanonical Lys 63-linked ubiquitin chains, playing important roles in signal transduction among eukaryotes. Ectopic expression of the cucumber UBC13 gene in Arabidopsis thaliana led to a more pronounced and Fe-responsive formation of branched root hairs, a key response of Arabidopsis roots to Fe deficiency. Plants carrying a mutation in the Arabidopsis ortholog UBC13A were unable to form branched root hairs upon Fe deficiency and showed a perturbed expression of Fe-regulated genes. Mutants defective in both Arabidopsis UBC13 genes, UBC13A and UBC13B, showed a marked reduction in root hair density. Mutations in the cognate E3 ligases RGLG2 and RGLG1 caused the constitutive formation of branched root independent on the iron supply, indicating the involvement of polyubiquitination in the altered differentiation of rhizodermal cells. It is concluded that UBC13, probably via the formation of Lys 63-linked ubiquitin chains, has a critical function in epidermal cell differentiation and is crucial for the regulation of Fe-responsive genes and developmental responses to Fe deficiency.

The present study was designed to compare the expression profile of two developmentally important genes (HSP-70.1 and GLUT-1) and total cell number (TCN) count in fast (group A) and slow (group B) cleaved buffalo embryos to access their in vitro developmental competence. Buffalo cumulus oocyte complexes (COCs) were collected from local abattoir ovaries and subjected to in vitro maturation in: TCM-199 supplemented with 10% FBS, BSA (3 mg/ml), sodium pyruvate (0.25 mM) and 20 ng/ml EGF at 38.5 0C under 5% CO2. In vitro derived embryos were collected at 4-8, 8-16 cell, morula and blastocyst stages at specific time points for gene expression analysis and total cell count. A semi-quantitative RT-PCR assay was used to determine the HSP-70.1 and GLUT-1 transcripts. Results showed that developmental competence and TCN count in fast (group A) cleaving embryos was significantly (P<0.05) higher than the slow (group B). The gene transcript of HSP-70.1 and GLUT-1 expressed in oocytes (immature and mature) and throughout the embryonic developmental stages in fast (group A) while in the slow (group B) cleaving embryos, the expression of HSP-70.1 was absent in all the embryonic developmental stages and expression of GLUT-1 was absent after 8-16 cell stage. In conclusion, TCN count and expression profile of HSP-70.1 and GLUT-1 genes in buffalo embryos are different taking into account the cleavage rate. Quality of such embryo for research purposes, TCN and expression profiling of developmentally important genes should be employed to optimize the in vitro culture system to produce superior quality of embryos.

ABSTRACT: BACKGROUND: Between embryonic day 12 and postnatal day 21, six major neuronal and one glia cell type are generated from multipotential progenitors in a characteristic sequence during mouse retina development. We investigated expression patterns of retina transcripts during the major embryonic and postnatal developmental stages to provide a systematic view of normal mouse retina development, RESULTS: A tissue-specific cDNA microarray was generated using a set of sequence non-redundant EST clones collected from mouse retina. Eleven stages of mouse retina, from embryonic day 12.5 (E12.5) to postnatal day 21 (PN21), were collected for RNA isolation. Non-amplified RNAs were labeled for microarray experiments and three sets of data were analyzed for significance, hierarchical relationships, and functional clustering. Six individual gene expression clusters were identified based on expression patterns of transcripts through retina development. Two developmental phases were clearly divided with postnatal day 5 (PN5) as a separate cluster. Among 4,180 transcripts that changed significantly during development, approximately 2/3 of the genes were expressed at high levels up until PN5 and then declined whereas the other 1/3 of the genes increased expression from PN5 and remained at the higher levels until at least PN21. Less than 1% of the genes observed showed a peak of expression between the two phases. Among the later increased population, only about 40% genes are correlated with rod photoreceptors, indicating that multiple cell types contributed to gene expression in this phase. Within the same functional classes, however, different gene populations were expressed in distinct developmental phases. A correlation coefficient analysis of gene expression during retina development between previous SAGE studies and this study was also carried out. CONCLUSIONS: This study provides a complementary genome-wide view of common gene dynamics and a broad molecular classification of mouse retina development. Different genes in the same functional clusters are expressed in the different developmental stages, suggesting that cells might change gene expression profiles from differentiation to maturation stages. We propose that large-scale changes in gene regulation during development are necessary for the final maturation and function of the retina.

Photochemical development was studied in developing cucumber (Cucumis sativus L. cv Hokushin) leaves to determine if the spatial pattern coincided with relative growth rates of expanding leaves, intercalary cell division, or position relative to the vascular tissue. Both leaf surfaces undergo a series of similar changes in chlorophyll a fluorescence kinetics, but the upper surface more quickly achieved the characteristic response. Imaging of fluorescence showed an individual developing leaf has four regions differing in kinetics, but these regions do not coincide with areas of increasing relative growth rate. Two of these regions lie at the leaf edge and their divergent kinetics may be related to structural and physiological features present at this position. A third area with different kinetics, in the basal region of the leaf, is spatially consistent with primordial regions that are clonal during development. The correspondence between areas of clonal growth and specific fluorescence kinetics indicates that cells of common ancestry show functional uniformity. No evidence was found that the proximity of the vascular tissue influenced development of photochemical function.

The effects of 2-chloroethylphosphonic acid (Ethrel), ethylene, and some growth retardants on sex expression of cucumber plants (Cucumis sativus L.) were investigated, with the use of a monoecious cultivar (Improved Long Green) which has a strong tendency toward maleness.Ethrel caused increased femaleness when applied at 50 milligrams per liter at the first to the third leaf stage, but when applied at the cotyledon stage it was ineffective. The later the time of application, the higher the node at which the first female flower appeared. The total number of female flowers was about the same regardless of application time. A mixture of gibberellins A(4) and A(7) caused maleness, and Ethrel caused femaleness. However, when applied in combination at the first leaf stage the interaction was not significant. It seems, therefore, that Ethrel and gibberellins are not antagonistic but rather have different sites of action, although they have opposing effects on sex expression.Ethylene caused femaleness but was far less effective than Ethrel. Alar (N-dimethylaminosuccinamic acid), CCC((2-chloroethyl)trimethylammonium chloride), Phosphon D(2, 4-dichlorobenzyl-tributylphosphonium chloride), and abscisic acid did not affect sex expression of cucumber.

Diffusates from seedlings and root exudates from 6-week-old plants of a monoecious line of cucumber, Cucumis sativus L., contained considerably higher levels of gibberellin-(GA-) like substances than did those from plants of an isogenic gynoecious line. Most of the GA-like activity was found in a chromatogram region typical of GA(1) and GA(3); some activity, particularly in root exudates, appeared also at an R(F) similar to that of GA(4) and GA(7).When seedlings were treated with (3)H-labeled GA(1), more radioactivity was found in the diffusates from monoecious seedlings than from gynoecious ones. The same was true of biological activity in root diffusates from older plants which had been treated with gibberellin A(4+7).In conjunction with evidence present in literature, these results support the idea that endogenous GAs play a part in the regulation of sex expression in cucumber, relatively high levels favoring the formation of staminate flowers.

Sex expression in cucumber (Cucumis sativus L.) and muskmelon (C. melo L.) was correlated with endogenous ethylene production. Plants of gynoecious (all female) sex types of the two species produced more ethylene than monoecius (male-female) plants. C. melo plants of a gynoecious sex type that normally produce only pistillate (female) flowers, when grown with hypobaric ventilation to facilitate removal of endogenous gases by diffusion, produced perfect (hermaphroditic) flowers. When either the plant was returned to atmospheric pressure or when the reduced-pressure ventilating stream was supplemented with ethylene, the same plants produced pistillate flowers. Enrichment of the atmosphere at either normal or reduced pressure with CO(2), a competitive inhibitor of ethylene action, also resulted in development of perfect flowers. Foliar application of a benzothiadiazole, a postulated inhibitor of ethylene action, resulted in formation of perfect flowers on gynoecious plants of C. melo and of staminate (male) flowers on gynoecious C. sativus. Based on these findings, it is proposed that ethylene is an endogenous regulator of sex expression in C. sativus and C. melo.

To understand the regulatory mechanisms governing unisexual flower development in cucumber, we conducted a systematic morphogenetic analysis of male and female flower development, examined the dynamic changes in expression of the C-class floral organ identity gene CUM1, and assessed the extent of DNA damage in inappropriate carpels of male flowers. Accordingly, based on the occurrence of distinct morphological events, we divided the floral development into 12 stages ranging from floral meristem initiation to anthesis. As a result of our investigation we found that the arrest of stamen development in female flowers, which occurs just after the differentiation between the anther and filament, is mainly restricted to the primordial anther, and that it is coincident with down-regulation of CUM1 gene expression. In contrast, the arrest of carpel development in the male flowers occurs prior to the differentiation between the stigma and ovary, given that no indication of ovary differentiation was observed even though CUM1 gene expression remained detectable throughout the development of the stigma-like structures. Although the male and female reproductive organs have distinctive characteristics in terms of organ differentiation, there are two common features regarding organ arrest. The first is that the arrest of the inappropriate organ does not affect the entirety of the organ uniformly but occurs only in portions of the organs. The second feature is that all the arrested portions in both reproductive organs are spore-bearing parts.